The invention relates to a process for the preparation of organosilanes.
GB 1 102 251 discloses the reaction of anhydrous alkali metal hydrogen sulphides with (haloalkyl)alkoxysilanes in a methanolic medium to give the corresponding mercaptoalkyl) alkoxysilanes at atmospheric pressure. The unusually long reaction time (96 h) for achieving high conversions and the unsatisfactory yield achieved are disadvantageous in this procedure.
It is known that mercaptoalkyl)alkoxysilanes can be prepared by the reaction of anhydrous alkali metal hydrogen sulphide with suitable (haloalkyl)alkoxy-silanes in the presence of a 10-100% molar excess of H2S (U.S. Pat. No. 5,840,952). Before the addition of the (haloalkyl)alkoxysilane, the alkali metal hydrogen sulphide is preferably formed by the reaction of alkali metal sulphide Me2S (Me—Li, Na, K) with H2S or by the reaction of H2S with alkali metal alcoholate. On the industrial scale, this process has the disadvantage that highly poisonous H2S has to be stored, metered and handled and the process is carried out in 2 stages, with the result that in principle the space-time yield of the process decreases.
It is furthermore. known that mercaptoalkyl) alkoxy-silanes can be prepared by reacting (haloalkyl)alkoxysilanes with anhydrous alkali metal hydrogen sulphide (NaSH) in polar, aprotic solvents (EP 0 471 164). The disadvantage of the process is that large amounts, at least 50% by volume, of solvent are used and this is toxic, for example in the case of dimethylformamide. In addition, the high boiling point of imethylformamide complicates the subsequent distillative working-up of the reaction products.
DE 103 517 35 discloses a process for the preparation of (mercaptoorganyl) alkoxysilanes, anhydrous, dried alkali metal hydrogen sulphide being reacted with a mixture of (haloorganyl) alkoxysilane and (haloorganyl)-halosilanes in an alcohol in a closed vessel in the absence of air and at an elevated pressure. The use of anhydrous alkali metal hydrogen sulphide is a disadvantage of this process.
EP 1130023 discloses the preparation of organosilylalkylpolysulphanes of the general formula(R1R2R3Si—R4—)2Sqfrom the organosilylalkyl halide of the general formulaR1R2R3Si—R4—X.
The reaction is carried out by initially introducing elemental sulphur and the organylalkyl halide in a polar organic solvent and adding anhydrous or virtually anhydrous ionic sulphide to the suspension. owing to the susceptibility of the Si-alkoxy bonds of the organosilylalkyl halide to hydrolysis, the ionic sulphides must be anhydrous or virtually anhydrous.
It is an object of the present invention to provide a process for the preparation of organosilanes which permits short reaction times in combination with good yields of crude product and in which water-containing sulphurization reagents can be used.